U.S. patent application number 09/392041 was filed with the patent office on 2001-12-20 for a process for isomerizing and dehydrogenating using a catalyst activated by sulfurization and passivation with ammonia or precursor thereof.
Invention is credited to ALARIO, FABIO, COUPARD, VINCENT, JOLY, JEAN-FRANCOIS, MAGNE-DRISCH, JULIA, MERLEN, ELISABETH.
Application Number | 20010053867 09/392041 |
Document ID | / |
Family ID | 9530309 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053867 |
Kind Code |
A1 |
MAGNE-DRISCH, JULIA ; et
al. |
December 20, 2001 |
A PROCESS FOR ISOMERIZING AND DEHYDROGENATING USING A CATALYST
ACTIVATED BY SULFURIZATION AND PASSIVATION WITH AMMONIA OR
PRECURSOR THEREOF
Abstract
Process for isomerization of a feedstock that contains aromatic
compounds with eight carbon atoms characterized in that it
comprises at least one isomerization stage a) that is carried out
in the presence of a catalyst that contains at least one metal of
group VIII and that is activated according to an activation process
that comprises at least one sulfurization stage and at least one
stage for passivation with ammonia, and at least one
dehydrogenation stage b).
Inventors: |
MAGNE-DRISCH, JULIA;
(VILETTE DE VIENNE, FR) ; COUPARD, VINCENT; (LYON,
FR) ; JOLY, JEAN-FRANCOIS; (LYON, FR) ;
ALARIO, FABIO; (NEUILLY SUR SEINE, FR) ; MERLEN,
ELISABETH; (RUEIL-MALMAISON, FR) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Family ID: |
9530309 |
Appl. No.: |
09/392041 |
Filed: |
September 9, 1999 |
Current U.S.
Class: |
585/482 ; 502/85;
502/86; 585/319; 585/480; 585/481; 585/906 |
Current CPC
Class: |
C10G 45/60 20130101;
C10G 59/02 20130101; C10G 65/043 20130101; Y10S 585/906 20130101;
B01J 2219/00006 20130101 |
Class at
Publication: |
585/482 ;
585/480; 585/481; 585/906; 585/319; 502/85; 502/86 |
International
Class: |
C07C 005/27; B01J
029/68 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 10, 1998 |
FR |
98/11.319 |
Claims
1. Process for isomerization of a feedstock that contains aromatic
compounds with eight carbon atoms that is characterized in that it
comprises at least one isomerization stage a) that is carried out
in the presence of a catalyst that contains at least one metal of
group VIII and that is activated according to an activation process
that comprises at least one sulfurization stage and at least one
stage for passivation with ammonia or with an ammonia precursor,
and at least one dehydrogenation stage b).
2. Process of isomerization according to claim 1, wherein the
feedstock that is treated in the isomerization stage contains at
least one compound that is selected from among ethylbenzene and
metaxylene.
3. Process of isomerization according to one of claims 1 to 2,
wherein the catalyst of stage a) contains at least one matrix, and
at least one additional element that is selected from among the
metals of groups III.A and IV.A of the periodic table.
4. Process of isomerization according to one of claims 1 to 3,
wherein the catalyst of stage a) contains at least one zeolite.
5. Process of isomerization according to claim 4, wherein the
zeolite that is contained in the catalyst of stage a) is selected
from the group that is formed by the mordenites, the omega zeolite,
the MFI-structural-type zeolites and the EUO-structural-type
zeolites.
6. Process of isomerization according to one of claims 4 or 5,
wherein the zeolite that is contained in the catalyst of stage a)
is the EU-1 zeolite of EUO structural type, whereby this zeolite
contains silicon and at least one element T that is selected from
the group that is formed by aluminum, iron, gallium and boron, such
that the overall atomic Si/T ratio is greater than 5, whereby said
zeolite is also at least partly in acid form.
7. Process of isomerization according to one of claims 4 or 5,
wherein the zeolite that is contained in the activated catalyst is
the MOR zeolite, whereby this zeolite contains silicon and at least
one element T that is selected from the group that is formed by
aluminum, iron, gallium and boron, such that the overall atomic
Si/T ratio is less than 20, whereby said zeolite is also at least
partly in acid form.
8. Process of isomerization according to one of claims 1 to 7,
wherein the process of activation of the catalyst of stage a)
comprises at least one stage of reduction of the metal compound
that is contained in the catalyst, at least one stage of
sulfurization and at least one stage of passivation with
ammonia.
9. Process of isomerization according to one of claims 1 to 8,
wherein the sulfurization stage of the activation process is
carried out before the introduction of the catalyst in the reactor
or on a catalyst that is already placed in the reactor, under a
neutral or reducing atmosphere at a temperature of about 20 to
500.degree. C., at an absolute pressure of about 0.1 to 5 MPa and
with a gas volume (inert or reducing) per volume of catalyst per
hour of about 50 to 600 h.sup.-1.
10. Process of isomerization according to one of claims 1 to 9,
wherein the sulfurization stage of the activation process is
carried out with at least one sulfur compound that is selected from
the group that is formed by hydrogen sulfide and the sulfur
compounds that can be decomposed to obtain hydrogen sulfide under
the conditions of the isomerization reaction.
11. Process of isomerization according to one of claims 1 to 10,
wherein the passivation stage of the activation process comprises a
fist step during which at least one injection is carried out of an
amount of about 0.02 to 5% by mass relative to the mass of the
catalyst, ammonia in vapor form or in the form of at least one
precursor compound of ammonia, at a temperature of about 20 to
300.degree. C., an absolute pressure of about 0.1 to 5 MPa, and in
the presence of an inert or reducing gas volume per volume of
catalyst per hour of about 50 to 600 h.sup.-1, and a second step
during which at least one continuous injection of ammonia is
carried out in vapor form or in the form of at least one precursor
compound of ammonia during the introduction of the feedstock that
is to be isomerized in an amount that corresponds to about 20 to
500 ppm by mass relative to the mass of the catalyst.
12. Process of isomerization according to one of claims 1 to 11,
wherein the passivation stage of the activation process is carried
out in the presence of hydrogen.
13. Process of isomerization according to one of claims 8 to 12,
wherein the reduction stage of the metal compound of the catalyst,
in the activation process, is carried out in the presence of
hydrogen that has a purity that is greater than or equal to 90 mol
%, at a temperature of about 300 to 550.degree. C., at a total
pressure of between atmospheric pressure and 3 MPa, whereby the
duration of the reduction is about 1 to 40 hours.
14. Process of isomerization according to one of claims 1 to 13,
wherein the isomerization reaction of stage a) is carried out at a
temperature of about 300 to 500.degree. C., at a partial absolute
hydrogen pressure of about 0.3 to 1.5 MPa, at a total absolute
partial pressure of about 0.4 to 2 MPa and at a P.P.H. (feedstock
weight/catalyst weight/hour) of about 0.2 h.sup.-1 to 10
h.sup.-1.
15. Process of isomerization according to one of claims 1 to 14,
wherein the catalyst that is used to carry out the dehydrogenation
reaction of stage b) comprises a substrate that contains at least
one refractory oxide, at least one noble metal of group VIII and at
least one element of groups I.A or II.A.
16. Process of isomerization according to one of claims 1 to 15,
wherein the catalyst that is used for carrying out the
dehydrogenation reaction of stage b) comprises at least one element
that is selected from the group that is formed by thorium and the
elements of groups IVa and IVb.
17. Process of isomerization according to one of claims 1 to 16,
wherein the dehydrogenation reaction of stage b) is carried out at
a temperature of about 300.degree. C. to 500.degree. C., at a
partial absolute hydrogen pressure of about 0.1 to 1.5 MPa, at a
total absolute partial pressure of about 0.2 to 2 MPa and at a
P.P.H. (feedstock weight/catalyst weight/hour) of about 0.20 to
18. ion according to one of claims 1 to 17, wherein a compound that
has a boiling point of about 80 to about 135.degree. C. is added to
the fresh feedstock in the form of recycling or in the form of
fresh compounds or in the form of recycling and fresh
compounds.
19. Process of isomerization according to claim 18, wherein the
compounds that are added represent about 0.1 to 20% by mass of the
total feedstock that enters the isomerization zone.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the area of the isomerization
processes of aromatic compounds with eight carbon atoms.
BACKGROUND OF THE INVENTION
[0002] According to the known processes for isomerization of
aromatic compounds with eight carbon atoms, a feedstock that is
generally low in paraxylene relative to the thermodynamic
equilibrium of the mixture (i.e., whose paraxylene content is
clearly less than that of the mixture with the thermodynamic
equilibrium at the temperature in question, whereby this mixture
comprises at least one compound that is selected from the group
that is formed by metaxylene, orthoxylene, paraxylene and
ethylbenzene) and generally rich in ethylbenzene relative to this
same mixture in thermodynamic equilibrium is introduced into a
reactor that contains at least one catalyst under suitable
temperature and pressure conditions to obtain a composition, at the
outlet of said reactor, of aromatic compounds with eight carbon
atoms that is as close as possible to the composition of said
mixture in thermodynamic equilibrium at the temperature of the
reactor.
[0003] Paraxylene and optionally orthoxylene, which are the desired
isomers because they exhibit an important advantage particularly
for the synthetic fiber industry, are then separated from this
mixture. Metaxylene and ethylbenzene can then be recycled to the
inlet of the isomerization reactor so as to increase the production
of paraxylene and orthoxylene. When it is not desired to recover
orthoxylene, the latter is recycled with metaxylene and
ethylbenzene.
[0004] The isomerization reactions of the aromatic compounds with
eight carbon atoms per molecule pose, however, several problems
that are produced by secondary reactions. Thus, in addition to the
main isomerization reaction, hydrogenation reactions are observed,
such as, for example, the hydrogenation of the aromatic compounds
of naphthenes, reactions of opening naphthene cycles that lead to
the formation of paraffins that have at most the same number of
carbon atoms per molecule as the naphthenes from which they are
obtained. Cracking reactions are also observed, such as, for
example, the cracking of paraffins that lead to the formation of
light paraffins that typically have from three to five carbon atoms
per molecule, dismutation and transalkylation reactions that lead
to the production of benzene, toluene, aromatic compounds with nine
carbon atoms per molecule (trimethylbenzenes, for example) and
heavier aromatic compounds.
[0005] All of these secondary reactions are greatly detrimental to
the yields of desired products.
[0006] The amount of secondary products that are formed (naphthenes
that typically contain from five to eight carbon atoms, paraffins
that typically contain from three to eight carbon atoms, benzene,
toluene, aromatic compounds with, for the most part, nine and ten
carbon atoms per molecule) depends on the nature of the catalyst
and the operating conditions of the isomerization reactor
(temperature, partial hydrogen and hydrocarbon pressures, feedstock
flow rate).
[0007] It is well known to one skilled in the art that in certain
catalytic processes, procedures for activating and/or selecting the
catalyst are necessary to optimize the performances of the
catalyst. For example, in the case of catalyst that contains a
metal of group VIII of the periodic table (Handbook of Physics and
Chemistry, 45th Edition 1964-65), such as, for example, platinum,
it is well known to pretreat the catalyst with hydrogen sulfide
(H.sub.2S) The sulfur that is contained in the hydrogen sulfide
molecule is attached to the metal and imparts to it improved
catalytic properties.
[0008] In addition, it has been shown that the secondary reactions
increase when the paraxylene content in the reactor is closer to
the paraxylene content in thermodynamic equilibrium under given
pressure and temperature conditions.
[0009] The optimization of the operating conditions and the
formulation of the isomerization catalyst make it possible to
improve the paraxylene yield but not to be loss-free.
SUMMARY OF THE INVENTION
[0010] The invention relates to a process for isomerization of a
feedstock that contains aromatic compounds with eight carbon atoms
that comprises at least one isomerization stage a) that is carried
out in the presence of activated catalyst according to the
particular procedure that is described below and at least one
dehydrogenation stage b). The process for activation of the
isomerization catalysts comprises at least one sulfurization stage
and at least one stage for passivation with ammonia.
[0011] It has actually been discovered that, on the one hand,
catalytic performance levels are improved when a catalyst is used
in a presulfurized form or a sulfurized form after introduction
into the reactor and that it is subjected to a passivation in the
presence of ammonia (NH.sub.3) or a precursor of ammonia and that,
on the other hand, it is possible to reach paraxylene contents that
are close to the paraxylene content in thermodynamic equilibrium
under given pressure and temperature conditions while reducing the
xylene losses by combining at least two reaction stages.
DETAILED DESCRIPTION OF THE INVENTION
[0012] According to a particular embodiment of this invention, the
feedstock that is treated in the isomerization stage contains at
least ethylbenzene or at least metaxylene or at least a mixture of
ethylbenzene and metaxylene.
[0013] Isomerization stage a) of the process according to the
invention uses an activated catalyst which, starting from a mixture
that contains aromatic compounds with eight carbon atoms including
xylenes and/or ethylbenzene, makes it possible to obtain a
composition--xylenes and ethylbenzene--that is close to that of the
composition of the mixture in thermodynamic equilibrium under given
temperature and pressure conditions.
[0014] The activation process of said catalyst pertains to all of
the catalysts for isomerization of aromatic compounds with eight
carbon atoms that contain at least one metal or metal compound of
group VIII that is selected from among iron, cobalt, nickel,
ruthenium, rhodium, palladium, osmium, iridium and platinum, and
preferably at least one noble metal or noble metal compound of
group VIII, preferably selected from among platinum and palladium.
This catalyst also comprises at least one matrix and optionally at
least one additional element that is a metal or a metal compound
that is selected from the complex that is formed by the metals or
metal compounds of groups III.A and IV.A.
[0015] The catalyst that is used in stage a) of the process
according to the invention is a supported catalyst and can contain
at least one zeolite that is preferably selected from among the
zeolites of mordenite structural type (MOR), MFI, EUO or mazzite,
such as, for example, the omega zeolite.
[0016] In a preferred form of the invention, the zeolite is of MOR
or EUO structural type, such as, for example, the EU-1 zeolite. The
EUO- or MOR-type zeolite contains silicon and at least one element
T that is selected from the group that is formed by aluminum, iron,
gallium and boron, preferably aluminum or boron. In the case of the
zeolite of EUO structural type, the overall atomic Si/T ratio is
greater than 5, preferably about 5 to 100. For the zeolite of MOR
structural type, the Si/T ratio is usually less than 20, and most
often between 5 and 15.
[0017] The zeolite of EUO or MOR structural type according to a
preferred embodiment of the invention is at least in part,
preferably virtually totally, in acid form, i.e., in hydrogen form
(H.sup.+), whereby the sodium content is such that the Na/T atomic
ratio is less than 0.5, preferably less than 0.1.
[0018] When the catalyst contains a zeolite, said zeolite
represents 1 to 90% by weight, preferably 3 to 60% by weight, and
even more preferably 4 to 40% by weight relative to the total
weight of the catalyst. The content by weight of said element(s) of
group VIII is generally from about 0.01 to 2.0% relative to the
total weight of the catalyst, preferably from about 0.05 to 1.0%
relative to the total weight of the catalyst. This element of group
VIII is preferably selected from the group that is formed by
platinum and palladium. Most often, this element is platinum.
[0019] The catalyst of stage a) of the process of this invention
optionally contains at least one additional element that is
selected from the complex that is formed by elements of groups
III.A and IN A VACUUM.A of the periodic table, preferably selected
from the group that is formed by tin and indium. The content by
weight of said element(s) is generally from about 0.01 to 2.0%
relative to the total weight of the catalyst, preferably from about
0.05 to 1.0% relative to the total weight of the catalyst.
[0020] A matrix (or binder) usually ensures the addition to 100% by
weight in the catalyst. It is generally selected from the group
that is formed by the natural clays (for example kaolin or
bentonite), synthetic clays, magnesia, aluminas, silicas,
silica-aluminas, titanium oxide, boron oxide, zirconia, aluminum
phosphates, titanium phosphates, zirconium phosphates, preferably
from among the elements of the group that is formed by the aluminas
and the clays. This matrix can be a single compound or a mixture of
at least two of these compounds.
[0021] The process for activation of the catalysts that are used in
stage a) that can isomerize aromatic compounds that contain eight
carbon atoms comprises at least one sulfurization stage and at
least one stage for passivation with ammonia that are carried out
in any order, whereby the sulfurization stage is generally preceded
by a stage of reduction of the metal compound that is contained in
the catalyst.
[0022] The sulfurization of the catalyst is carried out with a
sulfur compound, for example hydrogen sulfide or a hydrogen sulfide
precursor. The sulfurization of the catalyst can be carried out
before introducing said catalyst into the reactor; the catalyst is
then called a "presulfurized catalyst." It can also be carried out
on a catalyst that is already in place in the reactor.
[0023] In general, before sulfurization, the metal compound of
group VIII that is contained in the catalyst is reduced. This
presulfurization stage can be carried out by pure hydrogen sulfide
or by a preferably organic precursor of hydrogen sulfide, which
will then be decomposed in the reactor.
[0024] Without this list having a limiting nature, the sulfurized
organic compounds that can be used in the sulfurization stage are,
for example, the sulfurized alkyl compounds, the sulfurized aryl
compounds, and the sulfurized alkylaryl compounds. As examples,
butylethyl sulfide, diallyl sulfide, dibutyl sulfide, dipropyl
sulfide, dimethyl disulfide (DMDS), thiophene, dimethyl thiophene
and ethylthiophene will be cited.
[0025] The sulfurization stage of the catalyst is usually carried
out in a neutral or reducing atmosphere at a temperature of about
20 to 500.degree. C. and preferably about 60 to 400.degree. C., at
an absolute pressure of about 0.1 to 5 MPa and preferably about 0.3
to 3 MPa and with a gas volume (inert or reducing) per volume of
catalyst per hour (V.V.H.) of about 50 h.sup.-1 to 600 h-1 and
preferably about 100 to 200 h.sup.-1. Most often, the inert gas
that is used is nitrogen, and the reducing gas is usually most
often essentially pure hydrogen.
[0026] The sulfurization stage is associated with a passivation
stage in the presence of ammonia (NH.sub.3). The passivation can be
carried out before or after the sulfurization stage. In a preferred
way, the sulfurization stage is carried out before the passivation
stage. These two stages of sulfurization and passivation can be
carried out before or after the introduction of the catalyst in the
reactor. In a preferred way, the passivation stage in the presence
of ammonia is carried out whereas the catalyst is already in place
in the reactor.
[0027] The passivation with ammonia is carried out most often in
two periods: at least one injection of at least a specified amount
of ammonia, in NH.sub.3 vapor form, or in the form of a precursor
compound of ammonia, then at least one continuous injection of
ammonia in NH.sub.3 vapor form or in the form of at least one
precursor compound of ammonia during the introduction of the
feedstock that is to be isomerized. The duration of the injection
of the second ammonia period in NH.sub.3 vapor form of this ammonia
precursor depends on the duration of operation of the catalyst; in
particular it depends on the stabilization of temperatures within
the catalyst. The first injection is preferably carried out with
NH.sub.3 in vapor form, and the second injection is carried out
with at least one precursor compound of ammonia.
[0028] The precursors of ammonia (NH.sub.3) that can be used within
the scope of this invention are all the compounds that are known to
one skilled in the art that, in the presence of hydrogen, decompose
into ammonia that attaches to the catalyst. Among the compounds
that can be used, it is possible to cite the aliphatic amines, such
as, for example, n-butylamine.
[0029] According to a preferred embodiment of this invention, the
stages of sulfurization and passivation with ammonia are carried
out after the catalyst is charged in the reactor, and the
sulfurization stage is preceded by a catalyst reduction stage.
[0030] The reduction of the catalyst is carried out in the presence
of hydrogen that preferably has a purity that is greater than 90
mol %. The reduction temperature is about 300 to 550.degree. C. and
preferably about 400 to 520.degree. C. The total pressure is
between atmospheric pressure and 3 MPa, and preferably it is from
about 0.5 to 2 MPa. The duration of the reduction stage is usually
from about 1 to 40 hours and preferably from about 1 to 8
hours.
[0031] The hydrogen flow rate (addition of fresh hydrogen and
recycled hydrogen from the outlet to the inlet of the reactor) is
from about 0.1 l/h/g to 100 l/h/g of catalyst.
[0032] When the sulfurization stage in the presence of hydrogen of
the catalyst is carried out most often by using hydrogen sulfide
(H.sub.2S) as a sulfurizing agent, an amount of hydrogen sulfide
that corresponds to a content by weight of about 0.01 to 0.8% and
preferably from about 0.01 to 0.5% relative to the mass of the
catalyst is introduced into the reactor. The temperature, pressure
and hydrogen flow rate conditions are identical to those of the
reduction stage, in contrast, the hydrogen that is introduced into
the reactor is preferably only recycled hydrogen.
[0033] The passivation with ammonia during the first period of this
passivation is carried out by using gaseous ammonia or a precursor
compound of ammonia, in general mixed with hydrogen. The amount of
ammonia that is introduced into the reactor is from about 0.02 to
5% by mass and preferably from about 0.1 to 2% by mass relative to
the mass of the catalyst.
[0034] The temperature, pressure and hydrogen flow rate conditions
are identical to those of the reduction stage; in contrast, the
hydrogen that is introduced into the reactor is preferably only
recycled hydrogen.
[0035] The isomerization process of a feedstock that contains
aromatic compounds with eight carbon atoms comprises at least one
isomerization stage a) that is carried out in the presence of an
activated catalyst according to the preceding activation process
and that contains at least one metal of group VIII and preferably
at least one zeolite of EUO or MOR structural type, at least one
matrix and optionally at least one additional element and at least
one dehydrogenation stage b).
[0036] In the first stage of the isomerization process according to
this invention, the operating conditions of the isomerization zone
are selected to reduce the production of undesirable compounds that
are obtained from reactions that cause acid catalysis mechanisms
(cracking, dealkylation, dismutation, . . . ) to take effect. These
operating conditions are such that the production of naphthenes
with eight carbon atoms per molecule is significantly larger--about
10 to 30% by mass of the outlet effluent of the isomerization
zone--than the production that is obtained by standard
isomerization processes of aromatic compounds that contain eight
carbon atoms--which is generally from about 5 to 10% by mass of the
outlet effluent of the isomerization zone.
[0037] The effluent that is obtained at the end of the first
reaction stage is treated during a second stage in a reaction zone
that contains at least one dehydrogenation catalyst. The operating
conditions of this second stage can be different from or identical
to the operating conditions of the first stage, preferably the
operating conditions of these two stages are different. The
operating conditions of this second stage are determined so as to
obtain a composition of the mixture of xylenes and ethylbenzene
that is the closest possible to the composition in thermodynamic
equilibrium.
[0038] The catalysts for dehydrogenation of paraffins and
naphthenes are well known to one skilled in the art. The substrates
of these catalysts are generally refractory oxides; most often an
alumina is selected. These dehydrogenation catalysts comprise at
least one noble metal of group VIII of the periodic table and at
least one alkaline element or alkaline earth element of groups I.A
and II.A of the periodic table. Preferably, the noble metal of
group VIII that is selected is platinum, and the element of groups
I.A or II.A of the periodic table is selected from the group that
comprises magnesium, potassium, and calcium.
[0039] These dehydrogenation catalysts can also contain thorium
and/or at least one element M of groups IV.A or IV.B of the
periodic table. The elements of groups IV.A or IV.B are most often
selected from the group that is formed by tin, silicon, titanium
and zirconium. Some dehydrogenation catalysts also contain sulfur
and/or a halogen. More particularly, it is possible to use the
dehydrogenation catalysts that are described in U.S. Pat. Nos.
3,998,900 and 3,531,543 in the dehydrogenation stage of the process
according to this invention.
[0040] Without wanting to be tied to any particular theory, it is
noted that platinum exhibits a hydrogenolyzing activity that is
expressed to the detriment of the activity of the dehydrogenation
of naphthenes into aromatic compounds. This hydrogenolyzing
activity can be greatly reduced, and the selectivity of the
catalyst relative to the dehydrogenation reaction can be increased
by adding additional element M.
[0041] The refractory inorganic substrates that are used often have
an acidic nature and can generate undesirable secondary reactions,
such as cracking or isomerization reactions. This is why the oxide
substrate is generally neutralized by the addition of at least one
metal or an alkaline metal compound or an alkaline-earth metal
compound.
[0042] According to a preferred embodiment of this invention, at
least one compound that has a boiling point of about 80 to about
135.degree. C., preferably at least one compound that is selected
from the group that is formed by the paraffins with eight carbon
atoms per molecule, benzene, toluene, and naphthenes with eight
carbon atoms, is added to the feedstock that is introduced in the
isomerization zone.
[0043] This compound or these compounds are added to the feedstock
that is to be treated in the form of recycling and/or in the form
of fresh compounds in amounts such that the percentages per unit of
mass of added compounds relative to the total feedstock that enters
the reactor are usually as follows:
[0044] the percentage of paraffins with eight carbon atoms, in the
optional case where this compound is added, is from about 0.1 to
10% by mass, preferably from about 0.2 to 2% by mass,
[0045] the percentage of naphthenes with eight carbon atoms, in the
optional case where this compound is added, is from about 0.5 to
15% by mass, and preferably from about 2 to 8% by mass,
[0046] the percentage of toluene, in the optional case where this
compound is added, is from about 0.1 to 10% by mass, preferably
from about 0.2 to 5% by mass,
[0047] the percentage of benzene, in the optional case where this
compound is added, is from about 0.1 to 10% by mass, preferably
from about 0.2 to 2% by mass.
[0048] The percentage of total compounds that are added when
several compounds are added represents about 0.1 to 20% by mass and
often about 2 to 15% by mass relative to the total feedstock that
enters the isomerization zone.
[0049] According to a preferred embodiment of the invention, at
least two different compounds that each have a boiling point of
about 80.degree. C. to 135.degree. C. are introduced into the
reaction zone. More particularly, at least one naphthene with eight
carbon atoms and at least one paraffin with eight carbon atoms are
introduced. In another variant, when these compounds are obtained
from recycling of a liquid fraction that leaves the dehydrogenation
reactor, all of the compounds that are contained in this liquid
fraction that have boiling points of about 80.degree. C. to
135.degree. C. are introduced without being separated.
[0050] In the process of this invention, the isomerization stage is
used in the presence of hydrogen that can be introduced in the form
of fresh hydrogen, in the form of recycled hydrogen that is
obtained from the outlet of the isomerization zone or in the form
of recycled hydrogen that is obtained from the outlet of the
dehydrogenation zone. The operating conditions of the isomerization
stage are as follows: a reaction temperature of about 300 to
500.degree. C., preferably of about 320 to 400.degree. C., a
partial hydrogen pressure of about 0.3 to 1.5 MPa, preferably of
about 0.4 to 1.2 MPa, a total pressure of about 0.4 to 2 MPa,
preferably of about 0.6 to 1.5 MPa, and a P.P.H. (feedstock
weight/catalyst weight/hour) of about 0.2 to 10 h.sup.-1,
preferably of about 3 to 6 h.sup.-1.
[0051] In the process according to this invention, the
dehydrogenation stage is used in the presence of hydrogen that can
be introduced in the form of fresh hydrogen, in the form of
recycled hydrogen that is obtained from the outlet of the
isomerization zone or in the form of recycled hydrogen that is
obtained from the outlet of the dehydrogenation zone.
[0052] The operating conditions for the dehydrogenation stage are a
temperature of about 300 to 500.degree. C., preferably of about 400
to 420.degree. C., a partial absolute hydrogen pressure of about
0.1 to 1.5 MPa, preferably of about 0.4 to 1 MPa, a total absolute
pressure of about 0.2 to 2 MPa, preferably of about 0.5 to 1.5 MPa
and a PPH (feedstock weight/catalyst weight/hour) of about 0.2 to
10 h.sup.-1, preferably of about 3 to 6 h.sup.-1.
[0053] In addition, it is also possible to carry out a recycling of
aromatic compounds with eight carbon atoms that are contained in
the effluent of the dehydrogenation zone after the desired
compounds, i.e., paraxylene and optionally orthoxylene, have been
extracted.
DESCRIPTION OF THE DRAWING
[0054] FIG. 1 depicts a simple embodiment of the process according
to the invention.
[0055] According to this FIGURE, the feedstock that is to be
treated is introduced into isomerization zone R1 that comprises an
activated catalyst that contains an EUO- or MOR-structural-type
zeolite, at least one noble metal of group VIII, a matrix and
optionally at least one additional element via line 1.
[0056] Essentially pure hydrogen is introduced into line 1 via line
12, and the recycled hydrogen is introduced into line 1 via line
13. A purging of the hydrogen that circulates in line 13 is carried
out via line 15. The effluent of isomerization zone R1 is sent into
a separation zone S1 via line 2.
[0057] In S1, the hydrogen that is contained in the effluent is
isolated and recycled to the inlet of isomerization zone R1 via
line 13, and the remainder of the effluent is evacuated from this
separation zone S1 via line 3. This line 3 is equipped with a
pressure regulating valve V1. The fluid that is contained in line 3
is heated in a furnace F1 and then is evacuated from this furnace
via line 4. The effluent that leaves from the furnace via line 4 is
enriched with hydrogen that is recycled via line 14, and then this
mixture is introduced into dehydrogenation zone R2. The effluent of
zone R2 is sent via line 5 into separation zone S2.
[0058] In S2, the hydrogen that is contained in the effluent is
isolated and recycled to the inlet of dehydrogenation zone R2 via
line 14, and the remainder of the effluent is evacuated from
separation zone S2 via a line 6. A purging of the hydrogen that
circulates in line 14 is carried out via line 16.
[0059] The entire disclosure of all applications, patents and
publications, cited above and below, and of corresponding French
application 98/11.319, filed Sep. 10, 1998, are hereby incorporated
by reference.
[0060] The following examples illustrate the invention without
limiting its scope.
EXAMPLE 1
According to the Invention
[0061] A pilot unit is used that comprises two reactors in series
R1 and R2, whereby each is equipped with hydrogen recycling and a
pressure regulating valve is placed between the two reactors. Each
of the reactors is heated electrically and operates according to an
isothermal mode.
[0062] Each reactor contains 60 g of catalyst that is specific to
each stage.
[0063] The catalyst of the isomerization stage that is used in this
example is prepared according to the following procedure.
[0064] The base material that is used is an EUO-structural-type
zeolite, the EU-1 zeolite, raw straight from synthesis, that
comprises the organic structure, silicon and aluminum, and that has
an overall atomic Si/Al ratio that is equal to 13.6, a content by
weight of sodium relative to the dry EU-1 zeolite weight of 1.5%,
corresponding to an Na/Al atomic ratio of 0.6.
[0065] This EU-1 zeolite first undergoes a so-called dry
calcination at 550.degree. C. under a stream of air for 6 hours.
Then, the solid that is obtained is subjected to three ionic
exchanges in a 10N solution of NH.sub.4NO.sub.3 at about
100.degree. C. for 4 hours for each exchange.
[0066] At the end of these treatments, the EU-1 zeolite in NH.sub.4
form has an overall atomic Si/Al ratio that is equal to 18.3, a
content by weight of sodium relative to the dry EU-1 zeolite weight
of 50 ppm.
[0067] The EU-1 zeolite is then shaped by extrusion with an alumina
gel to obtain, after drying and calcination in dry air, substrate
S1 that consists of extrudates that are 1.4 mm in diameter and that
contains 10% by weight of EU-1 zeolite in H.sup.+ form and 90% of
alumina.
[0068] Substrate S1 that is thus obtained is subjected to an
anionic exchange with hexachloroplatinic acid in the presence of a
competing agent (hydrochloric acid) so as to introduce platinum in
the catalyst. The moist solid is then dried at 120.degree. C. for
12 hours and calcined under a flow of dry air at the temperature of
500.degree. C. for one hour.
[0069] The catalyst that is thus obtained contains 10.0% by weight
of EU-1 zeolite in H.sup.+ form, 89.7% of alumina and 0.29% of
platinum.
[0070] The dehydrogenation catalyst that is used for the second
stage of the process according to the invention is a catalyst with
an alumina base that contains 0.6% by mass of platinum, 0.9% by
mass of tin, 0.9% by mass of potassium and 0.6% by mass of
chlorine.
[0071] After charging, the isomerization catalyst is dried, then
the metal that is contained in the catalyst is reduced to
450.degree. C., then a sulfurization stage is initiated with
hydrogen sulfide (H.sub.2S) under a pressure of 16 bar
absolute.
[0072] To carry out this sulfurization, an amount of H.sub.2S that
is equal to 0.1% by mass relative to the mass of the catalyst is
introduced, and the temperature is then 380.degree. C.
[0073] After H.sub.2S is injected, the reactor is kept at
380.degree. C. for one hour with hydrogen recycling--without the
addition of fresh hydrogen. Then, the temperature of the reactor is
brought to 390.degree. C., and the temperature is increased
gradually for one hour. It then remains at 390.degree. C. for 2
hours.
[0074] Before ammonia is introduced, the temperature of the reactor
is gradually brought to 425.degree. C., and then this temperature
is maintained for one hour.
[0075] The amount of NH.sub.3 that is injected is equal to 0.25% by
mass relative to the mass of the catalyst. After the ammonia is
injected, the catalyst is left at 425.degree. C. for 2 hours with
hydrogen recycling. Then, the temperature of the reactor is
gradually reduced to 390.degree. C., and this reduction lasts for 2
hours.
[0076] With the temperature being stabilized at 390.degree. C., a
hydrogen flow rate of 10 nl/h (normal liters per hour) is
established. Then, the feedstock that is treated with 0.034% by
mass of n-butylamine is injected.
[0077] The feedstock that is to be converted is a mixture of
aromatic compounds with eight carbon atoms, and its composition is
given in Table 1 below.
[0078] The conditions of the injection of the feedstock that is to
be isomerized are as follows: a temperature of 390.degree. C., a
P.P.H. of 3 h.sup.-1 and a total pressure of 1.5 MPa.
[0079] In the dehydrogenation reactor (R2), the temperature is
400.degree. C. and the total pressure is 0.9 MPa.
[0080] In the tables below, the following abbreviations are used:
"C1-C8 paraffins" for paraffins that contain from 1 to 8 carbon
atoms, "C5 to C9 naphthenes" for naphthenes that contain 5 to 9
carbon atoms, and "C9+ aromatic compounds" for aromatic compounds
that contain nine or more carbon atoms.
1 TABLE 1 Compounds Inlet Outlet R1 Outlet R2 C1-C8 paraffins 0
0.61 0.75 C5 to C9 naphthenes 0 19.42 1.68 benzene 0 0.03 0.06
toluene 0 0.18 0.24 ethylbenzene 14.01 7.28 8.65 paraxylene 1.52
16.50 20.85 metaxylene 56.52 37.89 46.91 orthoxylene 27.95 17.58
20.19 C9+ aromatic compounds 0 0.51 0.67
EXAMPLE 2
For Comparison, Not in Accordance with the Invention
[0081] Each reactor contains 60 g of catalyst that is specific to
each stage that is described in Example 1.
[0082] The stages of reduction and sulfurization of the
isomerization catalyst of Example 1 are repeated identically. The
passivation stage by ammonia is not carried out, and n-butylamine
is not added into the feedstock.
[0083] The same feedstock is used under the same operating
conditions as those that are described in Example 1. The
compositions per unit of mass of the feedstock and effluent output
of each of the reactors is indicated in Table 2 below.
2 TABLE 2 Compounds Inlet Outlet R1 Outlet R2 C1-C8 paraffins 0
0.77 0.91 C5 to C9 naphthenes 0 20.59 2.20 benzene 0 0.04 0.07
toluene 0 0.26 0.32 ethylbenzene 14.01 7.20 8.58 paraxylene 1.52
15.99 20.36 metaxylene 56.52 37.23 46.69 orthoxylene 27.95 17.28
20.05 C9+ aromatic compounds 0 0.64 0.82
[0084] The results that are noted in Tables 1 and 2 very clearly
show the advantage that there is in using the process according to
this invention. The paraxylene production is high; it is 20.85% by
mass when the process according to the invention is used instead of
20.36% by mass when a process in 2 successive stages is used
without passivation by the ammonia of the isomerization
catalyst.
[0085] The yield of aromatic compounds with eight carbon atoms
increases from 95.68 to 96.60% by weight when the procedure of this
invention is applied.
[0086] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0087] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *